Comparative Morphometry of the Olfactory Bulb, Tract and Stria in the Human, Dog and Goat

Abstract

Morphometric parameters of olfactory brain components show species-dependent variations. However, the association of these parameters with olfactory function vis-à-vis ecological and evolutionary behaviors is poorly understood. I n this study, a morphometric analysis of the olfactory bulb, tract and stria was carried out in three ecologically diverse animals com prising humans (primate), dogs (carnivore) and goats (herbivore) to elucidate differences in morphometry in relation to olfactory funct ion. Using formalin-fixed brains, volumes and linear measurements of the olfactory structures were determined and correlated with th ose of cerebrum and the whole brain. The volume of the olfactory bulb was greatest in dogs, followed by goats and humans and constitut ed 0.31%, 0.18% and 0.01%, respectively, of the brain volume. Similarly, the ratio of volume of the bulb, tract and stria to that of brain was 1.95% in the dog, 0.77% in the goat and 0.03% in the human. The width of the bulb was greatest (p< 0.05) in dogs (10.80 ± 1.64mm) compared to goats (8.25 ± 0.96mm) and humans (5.50 ± 0.71mm), and accounted for a hemisphere breadth of 42.91%, 29.73% and 8.94% respectively. Interestingly though, the total length of the olfactory bulb, tract and striae increased in the order of goat (34 .5 ± 1.30mm), human (36.25 ± 1.70mm) and dog (48.20 ± 1.92mm), and constituted 21.47%, 51.87% and 72.30%, respectively, of the hemisphere length. These results suggest that the morphometric adaptations of the olfactory components to olfactory function decline from the dog, to goat, to human, and this may be indicative of the varied olfactory functional needs in regard to the ecological diversity of these sp ecies